Transdermal delivery of medication is not a new concept, as a variety of medications that are readily available for delivery through the skin have been available in ointment form for over thirty years. With ointments, however, it is difficult to achieve precise drug dosage. In a transdermal patch system, this problem is eliminated by controlling the rate of drug release over a prescribed perior of time. Patches are worn behind the ear, on the chest, or on the arm and dispense a drug for as long as a week at a time. For certain drugs transdermal delivery has significant advantages over oral administration. It eliminates "first pass" inactivation by the liver and irregular gastric absorption. Because of constant absorption through the skin, it maintains relatively constant blood levels of the drug.
Two drugs, scopolamine and nitroglycerin, have recently become commercially available in transdermal form. Although there are differences in composition and in the mechanism of drug delivery among the available transdermal delivery systems, they all appear to be functionally similar. Generally the systems have essentially steady state reservoirs sandwiched between an impervious backing and a membrane face. The systems usually are attached to the skin by an adhesive gel. Some products have a rate-controlling outer microporous membrane. One product depends on a diffusion matrix in which nitroglycerin molecules are in equilibrium between lactose crystals and the liquid phase. In another product, micropockets of nitroglycerin are evenly dispersed throughout a silicone polymer which controls the drug release rate and prevents dose dumping.
A description of the different commercial products which deliver nitroglycerin transdermally is set forth by Dasta, et al., American Pharmacy, NS22, 2, 29-35, Feb. 1982, which article also illustrates the various prior art nitroglycerin patches and their construction and operation, and which article is hereby incorporated by reference.
U.S. Pat. No. 4,336,243, issued June 22, 1982 describes transdermal nitroglycerin pads wherein the pad comprise a silicone polymer matrix being a cross-linked silicone rubber having from about 10 to 200 microns microseal compartments formed by the in situ cross-linking of the silicone rubber after it is admixed with a hydrophilic solvent containing the nitroglycerin in a hydrophobic solvent which enhances the dispersion and transport. U.S. Pat. No. 4,053,580, issued Oct. 11, 1977 describes an earlier pharmaceutical delivery device employing a silicone polymer matrix wherein the rate of release of the active ingredient is controlled by altering the solubility of the hydrophilic solvent system for the polymer matrix.
Another polymer diffusion matrix transdermal delivery system is described in published European patent application 80300038.9, of A. Keith entitled Polymeric Diffusion Matrix and Method of Preparation and Drug Delivery Device Comprising Said Matrix. This application describes a polymeric diffusion matrix composed of glycerol and polyvinyl alcohol together with a water-soluble polymer to provide a polymer matrix capable of sustained release of a drug dispersed in the matrix. Typically, the water-soluble polymer comprises a polyvinylpyrrolidone or a water-soluble cellulosic derivative. U.S. Pat. No. 3,797,494, issued Mar. 19, 1974 describes a transdermal bandage which includes a reservoir with a drug confined within the interior chamber of the reservoir and distributed throughout a reservoir matrix. In one embodiment the drug is released by a controlling microporous material, which microporous material meters the flow of the drug into the skin at a controlled rate. In another embodiment an adhesive coating is uniformly distributed through microcapsules comprising a drug encapsulated with a microporous rate controlling material.
While many transdermal drug delivery systems have been described as an economical and effective transdermal drug delivery system particularly for the delivery of contraceptive steroid drugs is still needed, and desired, particularly percutaneous delivery of steroid contraceptives in a controlled manner for periods of time ranging from one to four weeks or more.
Levonorgestrel is a synthetic steroid which has powerful progestational activity with minimal side effects at very low doses. Estradiol is a natural estrogen which has limited oral effectiveness because of "first pass" inactivation during circulation. On the other hand the synthetic steroid, ethinylestradiol, is active orally, since its inactivation by the liver and other tissues is very low. These contraceptives and others like Mestranol, Norethindrone, etc., are employed in various oral contraceptives manufactured in this country. Although levonorgestrel pills contain 150 micrograms of the drug, studies with implantable drug delivery systems indicate that only 30 micrograms per day are sufficient to prevent fertility.
Thus, it is desirable to provide an effective transdermal drug delivery system for the transdermal delivery of drugs, particularly contraceptive steroids.